For engine systems in vehicular or other mobile applications where a supply of hydrogen is required, due to challenges related to on-board storage of a secondary fuel and the current absence of a hydrogen refueling infrastructure, hydrogen is preferably generated on-board using a fuel processor. The hydrogen-containing gas from the fuel processor can be used to regenerate, desulfate and/or heat engine exhaust after-treatment devices, can be used as a supplemental fuel for the engine, and/or can be used as a fuel for a secondary power source, for example, a fuel cell.
One type of fuel processor is a syngas generator (SGG) that can convert a fuel into a gas stream containing hydrogen (H2) and carbon monoxide (CO), known as syngas. Air and/or a portion of the engine exhaust stream can be used as an oxidant for the fuel conversion process. The exhaust stream typically contains oxygen (O2), water (H2O), carbon dioxide (CO2), nitrogen (N2) and sensible heat, which can be useful for the production of syngas. Steam and/or water can optionally be added. The fuel supplied to the SGG can conveniently be chosen to be the same fuel that is used in the engine. Alternatively a different fuel can be used, although this would generally require a separate secondary fuel source and supply system specifically for the SGG. The H2 and CO can be beneficial in processes used to regenerate exhaust after-treatment devices. For other applications, for example, use as a fuel in a fuel cell, the syngas stream may require additional processing prior to use.
Syngas production can be segregated into three main processes: mixing, oxidizing and reforming, as illustrated in FIG. 1. The first process is the mixing process and it generally takes place at or near the inlet, where the oxidant and fuel streams are introduced into the SGG, in the so-called “mixing zone”. The primary function of the mixing process is to supply an evenly mixed and distributed fuel-oxidant mixture for subsequent combustion and reformation. If the fuel is a liquid it is typically atomized and vaporized, as well as being mixed with an oxidant in this zone. The next process, the oxidizing process, takes place downstream of the mixing zone, in the so called “combustion zone”. The primary function of the oxidizing process is to ignite the fuel-oxidant mixture to produce H2 and CO as primary products as well as the sensible heat required for downstream endothermic reformation reactions. The final process, the reforming process, is where oxidation products and remaining fuel constituents are further converted to H2 and CO via reforming reactions, in the so-called “reforming zone”. The syngas stream then exits the SGG and is directed for additional downstream processing and/or to the appropriate hydrogen-consuming device(s). There is not strict separation between the zones; rather, the zones transition or merge into one another, but the primary processes happening in each of the zones are typically as described above.
In vehicular or other mobile applications, an on-board SGG should generally be low cost, compact, light-weight and efficiently packaged with other components of the engine system. Some particular challenges associated with the design of fuel processors used in engine systems to convert a fuel and engine exhaust gas stream into a hydrogen-containing stream include the following:                (a) Engine exhaust stream output parameters, such as mass flow, pressure, temperature, composition and emission levels, vary significantly over the operating range of the engine.        (b) The output required from the fuel processor is typically variable. The hydrogen-containing gas stream is preferably generated as-needed in accordance with the variable demand from the hydrogen-consuming devices. This reduces the requirement for additional storage and control devices.        (c) Thorough mixing of the fuel and oxidant reactants is important. With liquid fuels, inadequate vaporization and mixing of the fuel with the oxidant stream can lead to localized fuel-rich conditions, resulting in the formation of coke or soot (carbon), residues and hot spots. At typical SGG operating temperatures, for example, 1000° C.-1200° C., the time to introduce and vaporize the fuel while effectively mixing the fuel with the oxidant stream is limited due to the extreme internal temperatures.        (d) The engine exhaust stream pressure is limited, especially at engine idle conditions. The pressure available to aid in the mixing and distribution of fuel with the oxidant stream is therefore limited under at least some operating conditions.        (e) High engine exhaust back-pressure can decrease the efficiency and performance of the engine, increasing the operating cost. Preferably, the pressure drop across the fuel processor and its associated components (for example, mixing and metering devices, and particulate filter) is therefore kept low.        (f) High system reliability and durability are typically required.        (g) The internal combustion engine exhaust after-treatment market has cost, volume, and weight constraints, particularly for vehicular applications.        
A cylindrical shaped reactor with a flow-through configuration, where a combined fuel and oxidant reactant mixture flows downstream predominantly in one direction axially through the cylinder, has been commonly used for fuel processors or SGGs. The shortcomings of these types of reactors include: portions of the reactor volume may not be fully utilized, additional devices may be required to promote mixing and/or distribution of the reactants, and additional devices may be required to stabilize the location of the combustion flame in the reactor. These shortcomings can increase the volume, weight, cost, and/or reduce the operating range of the fuel processor.
During a start-up process for a fuel processor, a secondary oxidant and fuel stream circuit or combustor are often employed to generate heat at lean or stoichiometric conditions, reducing the time for the fuel processor to reach a desired operating temperature. The secondary oxidant and fuel stream circuit or combustor used because an undesirable amount of carbon can be generated if the primary oxidant and fuel stream circuits are employed during the start-up process. However, the requirement for a secondary oxidant and fuel stream circuit or combustor increases the complexity, size, and cost of the fuel processor.
The present fuel processor with improved reactor design, components and operating methods is effective in addressing at least some of the issues discussed above, both in engine system applications and in other fuel processor applications.